The claimed invention belongs to heat exchange devices where the heat carriers do not mix, and may be used, for instance, in ventilation and air conditioning systems for heat exchange between the intake and the exhaust air streams.
A heat exchanger type fan is known, described in a Japanese application 60-75634, (Int. Cl. F 28 D 9/00, Filed Oct. 4, 1985, Publ. Date Jun. 7, 1994), consisting of a casing and two centrifugal fans mounted on the same shaft inside the casing but oriented in opposite directions in regard to each other. Two channels for heat carriers (air streams) of different temperature are formed in the casing, separated by a heat exchange element made as a corrugated radial partition installed beyond the edges of the impellers of the fans and equipped with a disk to separate the fans. When the fans rotate, the heat carriers enter the space between the blades of the fans and further on, passing over the corrugated radial partition of the heat exchange element on both sides, are removed from the casing via the respective blower outlets. Heat exchange takes place through the corrugated partition while the heat carriers pass over its faces. A big radial size should be listed among the disadvantages of such arrangement.
A heat exchanger type fan is known, described in a Japanese application 60-75635 (Int. Cl. F 28 D 9/00, Filed Oct. 4, 1985, Publ. date Jun. 7, 1994), consisting of a casing and two centrifugal fans mounted on the same shaft inside the casing, but oriented in opposite directions in regard to each other. Two channels for heat carriers of different temperature are formed in the casing, separated by a partition separating also both fans. The heat exchange element is made as radial fins mounted on both surfaces of the partition beyond the edges of the impellers of the fans. When the fans rotate, the heat carriers enter the interblade space of the fans via the suction inlets and further on, passing over both sides of the radial fins of the heat exchange element, are removed from the casing via the respective blower outlets. Heat exchange takes place through the radial fins and the partition itself Again a big radial size should be listed among the disadvantages of such arrangement.
The closest to the claimed invention is the heat exchanger type fan described in the Japanese application 61-86463 (Int. Cl. F 28 D 11/02, Filed Apr. 15, 1986, Publ. date Jan. 6, 1994), consisting of a casing and an impeller of a double-sided centrifugal fan made as a radially corrugated disk with an outer rim, the faces of the corrugation performing the function of radial blades. There is a partition in the casing adjoining the outer rim of the impeller and dividing the casing into two isolated chambers (channels) for heat carriers (air streams) of different temperature. Owing to this partition, there are two isolated centrifugal fans formed inside the casing with a single double-sided impeller. When the impeller rotates, the heat carriers enter the interblade space of the fans via the respective suction inlets and further on are removed from the casing via the respective blower outlets. Under such arrangement heat exchange takes place through the radial faces of the corrugated impeller.
In the known heat exchanger type fan the impeller, being the heat exchange surface at the same time, is formed by a radially corrugated surface. Such impeller design results in its low efficiency both as a part of a centrifugal fan and as a heat exchanger.
The former is explained by the fact that it is the radially corrugated surface that performs the function of the blades. In this case the air stream outgoing from the impeller of the fan has a surplus pressure exceeding that necessary pressure to overcome the total hydraulic resistance of the fan. This will require more power to be supplied. To eliminate this feature, characteristic of centrifugal fans with radial blades, blades of a different shape are required, namely backward-curved blades. It is obvious that manufacturing a corrugated disk with bent blades presents a rather difficult engineering problem. The curvature of such corrugation will be determined by the permissible plastic deformation of the material the impeller is made of With this the properties of the material will be in contradiction with the required rigidity of the impeller experiencing a considerable action of centrifugal forces during operation. This contradiction results in it being impossible to manufacture a corrugated disk with the degree of the blade curvature being great enough. Therefore with such arrangement it will be impossible to eliminate the surplus pressure and to reduce the amount of power to be supplied.
The low heat exchange efficiency of the known device is explained by the following. The heat exchange efficiency is to a certain extent influenced by both the area of the heat exchange surface and the rate at which the heat carrier passes over it. With radial blades, firstly, the area of heat exchange will be at its minimum, since the radial blades are of minimum length, and, secondly, the rate at which the heat carrier passes over that area will decrease towards the periphery of the impeller, which is caused, taking into account the continuity of the air stream, by the fact that the cross-section area of the interblade space increases towards its periphery. Thus, notwithstanding that the area of heat exchange is comparatively large, its efficiency is not going to be high.
Another factor behind the low efficiency of heat exchange is the direct-flow process implemented in the device where both heat carriers flow unidirectionally: in the known device they flow from the center to the periphery of the impeller. Whilst it is known that a better heat exchange efficiency can be achieved if the counter-flow pattern is used where the heat carriers flow in opposite directions. In regard to the known device this means that one of the impeller sides should work as a centripetal one. However, it is not possible with radial blades, and manufacturing a corrugated disk with bent blades, as it was already mentioned, presents a fairly complicated engineering problem, and, bearing in mind that the shape of the blades on both sides will be different, it will be impossible to make the impeller as a corrugated disk.
The engineering problem at the solution whereof the claimed invention is aimed, is to increase the efficiency of heat exchange and to lower the power consumption. Three embodiments of the solution for the stated problem are claimed.
The essence of the claimed invention according to the first embodiment consists in that in a heat exchanger type fan comprising a casing and an impeller of a double-sided centrifugal fan mounted in it, the casing being divided into two isolated chambers which, together with the impeller, form two isolated centrifugal fans, in accordance with the invention the impeller is made as a solid dividing disk on both sides whereof blades are made normal to its plane, said blades being bent backwards (backward-curved).
Replacement of the corrugated impeller disk with a solid disk with the blades made normal to its surface on both its sides will allow for the manufacturing of the blades of any desired curvature, such arrangement being no longer dependent on the manufacturing technology for the corrugated surface. The fact that the blades are made bent backwards permits to make the surplus pressure at the outlet of the centrifugal fan considerably lower, thus reducing the amount of power consumed. Changing the curvature of the blades it becomes possible to change the cross-section area of the interblade space normal to the blades, to seek for the constant rate of the airflow passing over the blade surfaces. Manufacturing the blades this way, as distinct from the known one, will make it possible to considerably increase both the number of the blades and xe2x80x9cthe density of the impeller blade spacingxe2x80x9d, that is, the ratio of the blade length to the distance between the blades on the mid-radius, thus effectively raising the efficiency of heat exchange. Notwithstanding the fact that in the claimed fan design heat exchange between the two air streams takes place in addition through an introduced dividing disk, the possibilities for the modification of the blades of the impeller offered by the new design of the latter, to a large extent compensate the decrease in the heat exchange efficiency caused by the introduction of the additional dividing disk.
In order to noticeably increase the heat exchange efficiency in the claimed device, it makes sense to manufacture the blades with the ratio of their length that is determined by the bisecting line of blade profile to the distance between the blades over the mid-radius being no less than 10.
In order to increase the heat exchange area between the impeller blades additional intermediate blades can be installed over the periphery of the dividing disk
In addition, the impeller blades may be made with a constant width of the interblade channel to provide for the uniform rate of the heat carrier flow in the interblade channel and, accordingly, to raise the efficiency of heat exchange.
Additionally, the fans may have a front disk attached to the blades, with an axial passage to let the heat carrier through into the interblade space. The front disk encloses the interblade space, thus reducing the fan losses and increasing the efficiency of heat exchange.
The blower outlets of both fans may be made axisymmetric and turned in the axial direction towards the side opposite to the respective suction inlet. Such arrangement will ensure that the heat carriers pass from the one to the opposite side of the device. This will considerably facilitate the installation of the claimed heat exchanger type fan in the systems of ventilation and air conditioning, corresponding to the direction of the input and the exhaust airflows.
The essence of the claimed invention according to the second embodiment consists in that in a heat exchanger type fan comprising a casing and a two-sided impeller mounted in it, on one side whereof the blades of a centrifugal fan are arranged, the casing being divided into two isolated chambers which, together with the impeller, form two isolated sections, one of which being a centrifugal fan, in accordance with the invention the impeller is made as a dividing disk, the above-mentioned blades of the centrifugal fan being arranged on one side of the dividing disk, while on its other side the blades of a centripetal fan are made, in the aggregate forming the above-mentioned two-sided impeller, one side whereof serving as the impeller of said centrifugal fan, and the other onexe2x80x94as that of the centripetal fan.
Replacement of the corrugated impeller disk with a solid disk with the blades made on both its sides will allow for the manufacturing of the blades of any desired shape, such arrangement being no longer dependent on the manufacturing technology for the corrugated surface. Specifically, on one side of the impeller centripetal blades are made, which provides for its operation as a centripetal fan. In this case the most efficient counter-flow heat exchange pattern is implemented. Changing the curvature of the blades it becomes possible to change the cross-section area of the interblade space normal to the blades, to seek for the constant rate of the airflow passing over the blade surfaces. Manufacturing the blades this way, as distinct from the known one, will make it possible to considerably increase both the number of the blades and xe2x80x9cthe density of the impeller blade spacingxe2x80x9d, that is, the ratio of the blade length to the distance between the blades on the mid-radius, thus effectively raising the efficiency of heat exchange. Notwithstanding the fact that in the claimed fan design heat exchange between the two heat carriers takes place in addition through an introduced dividing disk, the counterflow heat exchange pattern and the possibilities for modification of the blades of the impeller offered by the new design implementation of the latter, not only compensate for the decrease in the heat exchange efficiency associated with the introduction of the additional dividing disk, but enhance this parameter of the device on the whole.
To lower the surplus pressure at the outlet of the centrifugal fan and the inlet of the centripetal fan, the blades should be made bent backwards (backward-curved).
As with the first embodiment, in order to increase the heat exchange area it is expedient to manufacture the blades of the fans with the ratio of their length to the distance between the blades over the mid-radius being no less than 10.
As with the first embodiment, in order to increase the heat exchange area between the blades of the fans, intermediate blades may be installed over the periphery of the dividing disk
As with the first embodiment, the impeller blades may be made with a constant width of the interblade channel to provide for the uniform rate of the heat carrier flow in the interblade channel and, accordingly, to raise the efficiency of heat exchange.
In addition, the impeller of the centrifugal fan may have a solid front disk (impeller shroud) attached to the blades, and the dividing disk may have an axial passage, around which the outlet of the centripetal fan can be made, connected to the interblade space of the centrifugal fan impeller. With this the above-mentioned outlet of the centripetal fan shall be located inside the suction inlet of the centrifugal fan. Such configuration will ensure that the heat carriers pass from the one to the opposite side of the device, thus facilitating its installation, for instance, in the systems of ventilation and air conditioning, corresponding to direction of the input (or the exhaust) airflow.
As with the first embodiment, the impeller of the centrifugal fan may have a front disk (impeller shroud) attached to the blades, with an axial passage to let the drawn-in heat carrier into the interblade space of the centrifugal fan. The front disk (impeller shroud) encloses the interblade space, thus reducing the fan losses and increasing the efficiency of heat exchange.
Besides, in order to reduce losses at the input, an inlet may be arranged around the axial passage of the impeller front disk (impeller shroud) of the centrifugal fan, said inlet being connected to the interblade space of the centrifugal fan impeller; at that this inlet should be installed inside the suction inlet of the centrifugal fan with a minimum gap allowed, said gap to be selected so that during rotation of the centrifugal fan the outside surface of the above-mentioned inlet would not come into contact with the suction inlet. Also, the impeller of the centripetal fan may have a solid front disk attached to the blades, and the dividing disk may have an axial passage, around which the outlet of the centripetal fan can be arranged, connected to the interblade space of the centripetal fan impeller, the above-mentioned outlet of the centripetal fan located inside the inlet of the centrifugal fan. As shown above, such configuration ensures that the heat carriers pass from the one to the opposite side of the device.
The essence of the claimed invention according to the third embodiment consists in that in a heat exchanger type fan comprising a casing and a two-sided impeller mounted in it, on one side whereof the blades of a centrifugal fan are arranged, the casing being divided into two isolated chambers which, together with the impeller, form two isolated sections, one of which being a centrifugal fan, in accordance with the invention the impeller is made as a dividing disk, the above-mentioned blades of the centrifugal fan being arranged on one side of the dividing disk, while on its other side turbine blades are arranged, in the aggregate forming the impeller, one side whereof serving as the impeller of the above-mentioned centrifugal fan, and the other onexe2x80x94as that of the centripetal turbine.
Like with the previous embodiments, replacement of the corrugated impeller disk with a solid disk with the blades on both its sides will allow for the manufacturing of blades of any desired shape, such arrangement being no longer dependent on the manufacturing technology for the corrugated surface. Centrifugal blades are arranged on one side of the impeller to provide for its operation as a centrifugal fan, and the blades of a centripetal turbine on the other side. In this case the most efficient counter-flow heat exchange pattern is implemented. Like with the previous embodiments, changing the curvature of the blades it becomes possible to change the cross-section area of the interblade space normal to the blades, seeking for the constant rate of the airflow passing over the blade surfaces, as well as to increase considerably both the number of the blades and xe2x80x9cthe density of the impeller blade spacingxe2x80x9d.
Besides, arranging turbine blades on one side of the impeller will make it possible to use the claimed device in the systems with an external blower, thus further reducing the power consumption due to the fact that the heat carrier entering via the inlet of the turbine under pressure, will rotate the impeller. At a certain pressure it might be sufficient to provide for the impeller rotation without using an additional drive.
To enhance the performance of the device, a blower may be additionally installed in the inlet of the turbine. At that in one of the particular cases of embodiment of the idea the inlet of the turbine is made as a ring-shaped orifice coaxial to the impeller, and the blower is made as an axial fan whose blades overlap the above-mentioned ring-shaped orifice of the turbine inlet. In another case the inlet of the turbine is made as an orifice in its peripheral part, and the blower is made as a centrifugal fan installed in this orifice.
As with the previous embodiments, to lower the surplus pressure at the outlet of the centrifugal fan and the inlet of the turbine, the respective blades should be made bent backwards (backward-curved).
As with the previous embodiments, in order to increase the heat exchange area, the blades of the centrifugal fan and/or blades of the centripetal turbine shall be manufactured with the ratio of their length to the distance between the blades over the mid-radius being no less than 10.
As with the previous embodiments, in order to increase the heat exchange area between the blades of the centrifugal fan and/or blades of the turbine, intermediate vanes may be installed over the periphery of the dividing disk
As with the previous embodiments, the blades of the centrifugal fan and/or blades of the turbine may be made with a constant width of the interblade channel to provide for the uniform rate of the heat carrier flow in the interblade channel and to raise, accordingly, the efficiency of heat exchange.
As with the second embodiment, a configuration to ensure that the heat carriers pass from the one to the opposite side of the device is also possible. For that purpose the impeller of the turbine may have a solid front disk attached to the blades, and the dividing disk may have an axial passage, around which the outlet of the turbine can be arranged, connected to the interblade space of the turbine impeller. With this the above-mentioned outlet of the turbine shall be located inside the suction inlet of the centrifugal fan.
As with the previous embodiments, in order to reduce the fan losses and increase the efficiency of heat exchange, the impeller of the centrifugal fan may have a front disk (impeller shroud) attached to the blades, with an axial passage to let the drawn-in heat carrier into the interblade space of the centrifugal fan.
As with the second embodiment, in order to reduce losses at the input, an inlet can be arranged around the axial passage of the impeller front disk (impeller shroud) of the centrifugal fan, said inlet being connected to the interblade space of the centrifugal fan impeller, at that this inlet should be installed inside the suction inlet of the centrifugal fan with a minimum gap allowed. In this case the impeller of the turbine may also have a solid front disk (impeller shroud) attached to the blades, and the dividing disk may have an axial passage, around which the outlet of the turbine can be arranged, connected to the interblade space of the turbine impeller, the above-mentioned outlet of the turbine located inside the inlet of the centrifugal fan.
The presence of a centripetal turbine permits, in the latter configuration of the inlet and the outlet of the centrifugal fan, as well as of the inlet and the outlet of the turbine, to implement a two-stage heat exchange pattern. In this case the described device will serve as the first stage, complemented with the second identical stage, both stages being installed coaxially and with the front disks of the turbines towards each other, while the blower outlets of the centrifugal fans of one stage are connected to the inlets of the turbines of the other stage. With this, the suction inlet of the first stage and the outlet of the second stage will respectively serve as the inlet and the outlet for one heat carrier, while the suction inlet of the second stage and the outlet of the first stage will respectively serve as the inlet and the outlet for the other heat carrier. With this combination of two identical devices the centrifugal fan of one of those (of one stage) will deliver the stream of one of the heat carriers to the turbine of the other device. The transfer of the other heat carrier will proceed in the opposite direction. Heat exchange between the heat carriers will take place as stated abovexe2x80x94according to the counter-flow pattern.
The latter particular design of the third embodiment of the invention applied herein enables one, on the one hand, to considerably enhance the heat exchange (this is so because heat carriers pass two heat-exchange stages) and, on the other hand, to optimize the size of two-stage device (this is so because in this case impellers could be installed on one shaft and no additional blowers are needed for the purpose of turbine rotation). Additional decrease in the device size and weight can be attained due to making front disks of the turbines of both stages as a single unitxe2x80x94that is in the form of one disk.